Cottonwood Leaf Beetle

The City of Aspen has identified a native insect pest called cottonwood leaf beetle which has had a seasonal population surge two years in a row. Due to the unprecedented nature of this occurrence, the city is evaluating measures to mitigate potential impacts to our cottonwoods in the community forest if the surges in the insect’s population continues to occur. The Aspen Parks Department will be mapping the impacts of the insect during the late summer to be able to track changes over the coming years. It is uncertain at this time whether this will be a recurring problem.


Q: “Why is it causing trees turning brown around town?”

A: “The leaf browning is caused when the beetle larvae chews on the leaves of cottonwoods and turns them brown. If you look closely at a leaf, you will see that the veins or “skeleton” of the leaves will be left intact. The adult beetles generally cause less feeding damage as they chew around the edges of leaves.

Q: “Are the all the trees dying??”

A: “No, even though it appears as though the trees are dead or dying, they are only being temporarily defoliated. Most of the time with this insect, the browning leaves are more of a nuisance than anything. Our staff is looking into the recent surge of the insect and are determining if any action is needed.

Q: Is there anything I should do for my trees?

A: Make sure your tree(s) get adequate water during from Spring to Fall. At this time, the Parks Department is still assessing the extent of the damage. While experts say that treatment is not usually warranted, cottonwood trees which have already been impacted or are in a weakened state may be good candidates for systemic insecticides or other control methods. If you would like further information or assistance, you can contact your local arborist or reach out to the City Forester at

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